Diseased garrya eliptica

My garrya eliptica has a brown spot and the leaves are all dry and brittle. I sited it in a north facing position with a west wall behind it. My soil is free draining. It was staked firmly and has been in situ for about three years. I was out of the country from mid october until mis november but my sons could not say if there had been a frost or not. It was looking lovely and I hope I am not going to lose it. Does anyone have any helpful suggestions please?